1. Field of the Invention
This invention relates generally to power distribution systems and, more particularly, to a method and apparatus for control of circuit protection devices.
2. Description of the Prior Art
In power distribution systems, power is distributed to various loads and is typically divided into branch circuits, which supply power to specified loads. The branch circuits also can be connected to various other power distribution equipment, transformers, which step down the supply voltage for use by a specific piece of electrical equipment.
Due to the concern of an abnormal power condition in the system, i.e., a fault, it is known to provide circuit protective devices to protect the various loads, as well as the power distribution equipment. The circuit protective devices, e.g., circuit breakers, seek to prevent or minimize damage. The circuit breakers also seek to minimize the extent and duration of electrical service interruption in the event of a fault.
It is further known to utilize lockout mechanisms for circuit breakers that interact with the circuit breaker operating mechanisms to prevent the breaker contacts from being closed until the lockout mechanism is manually reset. Such lockout mechanisms also include solenoids having biased plungers that immediately return to their home position when the solenoid is de-energized.
Such lockout mechanisms suffer from the drawback of requiring manual intervention to reset the mechanism and enable the closing of the circuit breaker. These lockout mechanisms also suffer from the drawback of requiring continuous energizing of the solenoid to maintain the circuit breaker in the desired lockout state. In circuits having protection systems incorporating such mechanisms, loss of power and/or loss of communication within the protection system can result in unwanted changes to the lockout state of the breakers of the protection system. Such changes can occur regardless of the duration of the loss of power and/or loss of communication, and regardless of the extent of the loss of power and/or loss of communication throughout the system.
Accordingly, there is a need for circuit protection devices that reduce the risk of damage to a circuit in the event of a loss of power and/or a loss of communication within the protection system incorporating the circuit protection devices. There is a further need for protection systems having lockout devices that do not require continuous signals or energy to maintain a desired state or configuration of protection, and which are stable in a given lockout state.